Why transition metals show catalytic properties?

Explanation

Many transition metal and their compound are found to acts as catalyst. Because of the presence of the incompletely d-subshell. They can form unstable intefl)lediate give reaction path oflower activation energy and therefore increase the rate ofreaction.
For Example : 1. Iron and molybdenum are used as catalyst in the manufacture of ammonia from `N_2 and H_2` in Haber process.
`N_2(g) + 3H_2(g) overset(Fe or Mo) hArr 2 NH_3 (g)`